I would not call that strange behavior, I'd call that expected resultsOverlapping 2 objects is not proper CAD modeling for 3D printing. As such the overlapping space and geometry is actually an invalid object and so null. So it didn't slice it.

Again, actually expected. The results show that because it ends up as 2 objects that are valid but spaced the skirt surrounds the individual objects- again expected behavior.

Last edited by Jetguy on Tue May 01, 2018 12:16 am, edited 1 time in total.

Also here, but the picture is what matters https://www.shapeways.com/tutorials/pre ... d_printingHere you have 2 intersecting cubes. What this is not showing is a layer slice view but the concept is the same, 2 overlapping squares leaves a rectangle in the middle that is the massive unknown land. At a layer level, the basic rules for infill are broken because the leftover "hidden" geometry still exists. Should the shell follow that geometry? Which side is infill (center rectangle, 2 outer rectangles, or all 3)?

shell_composite.gif (13.66 KiB) Viewed 396 times

Again, what they do in the second image is remove the hidden and conflicting internal geometry to make all walls contiguous and facing out thus making the entire center space "infill".

I guess my issue with that is, enabling that, what we are doing is basically conforming to a non-standard arrangement of STLs.

Teaching folks it's OK to overlap- don't worry about hidden geometry, this is just not good practice.Here's the why on this. CAD and CAM, 3D printing, this is all an exact science right? Perfect numbers, exact dimensions, you want it to be accurate and true right? So then when you blow past the basic rules, and you export or merge a non conforming STL file, or files in this case and intentionally overlap them, well it's just a sloppy way of doing this. You are hoping, praying that the slicer "figures out" what you really wanted, because the STL input file you gave it has errors and is open to all kinds of alternate interpretation of what is infill, what is a void open space, where a wall should be, shells go on the inside or outside of that wall? Again, it's just sloppy train of thought.

I'm not knocking Raise 3D for adding that feature and sure, sometimes, you play around, want to merge 2 objects and it's an easy way to roll the dice and maybe you get what you want with minimal effort. But it's just not something we should depend on for most prints, and certainly not anything critical where open interpretation can lead to voids and other defects in the printed object due to serious flaws in how and what was deemed as infill and shells. Again, I just think it's imperative we teach everyone "the right way" and then sure, if you want to use the experimental way, that's a great thing too. What I'm saying is, Raise 3D needs to beef up the FAQ and how to print section and training of the website and documentation. This is only going to get buried, and then come up as another new user question some time in the future.